Pitt Logo

dept. of structural biology


VAN DER WEL HOME


RESEARCH

Solid State NMR

Protein & Amyloid

Protein-Lipid Interaction

SSNMR Methods


Publications

Teaching

Positions

Selected Links


Contact info


web site hit
counter


CLICK HERE FOR CURRENT WEBSITE


Membrane Protein-Lipid Interactions


Below I describe some of my previous research on transmembrane helices and Trp anchoring:

Many integral membrane proteins have a membrane spanning region that is characterized by the presence of predominantly hydrophobic residues, but is flanked by specific characteristic residues. This is illustrated below for selected membrane proteins crystal structures, where we see a clear pattern of distribution of the tryptophan trp and tyrosine tyr residues near the membrane interface, where they appear to act as interfacial anchors.

Potassium Channel (1bl8) Maltoporin (1af6) Outer Membrane Phospholipase A (1qd5) ompX (1qj9) PhoE (1pho)

The helices that constitute the membrane spanning domain of many of these proteins often display a specific tilt relative to the membrane. This can be functionally important, and has helix tilting has been found to be involved in the functioning of various membrane proteins. In addition, tilting is one of the ways in which the hydrophic mismatch between a protein and surrounding lipids can be adjusted. During my PhD in the lab of Roger Koeppe II, we studied various aspects of protein-lipid interactions in detail, through the use of model transmembrane peptides. (WALP peptides) that feature model a a helical core of hydrophobic amino acids, surrounded by interfacial anchors. Using solid state NMR methods using macroscopically aligned membranes, we were able to study both their tilt and the behavior of their Trp interfacial anchors, while in a proper, hydrated lipid bilayer environment. The use of 2H NMR on transmembrane helices containing deuterated Ala [2] residues allowed a direct measurement of their tilt angles, whereas similar measurements where the Trp residues were deuterated provided insights into these residues. 

Aligned samples and 31P NMR

Additional measurements on lipid liposomes allowed us to see the remarkable effect of these peptides on the phospholipid phase transitions, as monitored by 31P-NMR. They were found to lead to the increased induction of inverted, non-bilayer structures, which was correlated to the extent of hydrophobic mismatch. Interestingly, the formation of non-bilayer phases is thought to be essential for biological processes that involve membrane fusion and fission. 

WALP19:
acetyl-GWWLALALALALALALWWA-ethanolamin
e


Bilayer to hexagonal phase transition

Figure of WALP16, WALP23 and WALP31


References

  1. Van der Wel, P.C.A. et al. (2000)  "Tryptophan-anchored transmembrane peptides promote formation of nonlamellar phases in phosphatidylethanolamine model membranes in a mismatch-dependent manner." Biochemistry 39: 3124-33. *
  2. Van der Wel, P.C.A. et al. (2002) "Geometry and intrinsic tilt of a tryptophan anchored membrane spanning peptide by 2H NMR." Biophys. J. 83: 1479-1488 *
  3. Van der Wel, P.C.A. et al. (2007) "Orientation and motion of tryptophan interfacial anchors in membrane-spanning peptides." Biochemistry 46: 7514-7524 *